The presence or absence of specific cell surface receptors on mammalian cells play a role in vitro and are believed to be important in vivo, in the species and tissue specificity of virus diseases of man and other animals. In spite of this, the molecular structure and normal cellular functions of cellular receptors for viruses are poorly understood. Different strains of mammalian reoviruses and reassortants derived from the two parent strains, have different cellular tropisms (including neural cell tropism) in an in vivo murine model, and different receptor specificity for host cells in vitro. We plan to exploit the reovirus system, to determine at a molecular level the host cell surface components which promote attachment and entry of different serotypes of reovirus into susceptible cells in vitro and in vivo, in an effort to elucidate for one virus system, the molecular basis of cellular and tissue tropism. Proposed studies include: (1) Specific Sialyloligosaccharide Requirement on Host Cell Glycoproteins and/or Glycolipids for Reovirus Binding and Infectivity. These experiments will involve restoration of infectivity for reoviruses by enzymatic resialylation, and by the incorporation of highly purified gangliosides into the cell membranes of desialylated host cells. (2) Receptor Negative Cells for Reovirus. As for desialylated host cells, we will study the effect of ganglioside incorporation into host cell membranes, on the ability of reoviruses to bind to and infect reovirus resistant, receptor negative cells. (3) Binding of Reoviruses to Purified Gangliosides and Sialoglycoproteins. We will continue to characterize the sialyloligosaccharide specificity of reovirus sigma 1 polypeptides, by their ability to bind directly to highly purified gangliosides and sialoglycoproteins of defined sequence. (4) Receptor Variants. We are attempting to select reovirus strains which are resistant to the effects of sialoglycoprotein attachment and infectivity inhibitors, to determine if viral sialyloligosaccharide binding specificity is important for receptor specificity and tissue tropism in vivo. (5) Binding of Reovirus or Viral Attachment Proteins to Plasma Membrane Components. We plan to study the neuraminidase and glycosidase sensitive and resistant, reovirus binding components present in reovirus receptor positive and negative host cells, in an effort to define components which are important for reovirus binding to and infection of host cells. (6) Monoclonal Antibodies. Antibodies recognizing different specific sialyloligosaccharide sequences or protein components of host cells will be selected (or obtained) and tested for their ability to inhibit virus attachment and infectivity.